1. Field of the Invention
This invention relates to the phenylpyrimidine derivatives useful as a principal component of ferroelectric liquid crystals or compositions thereof, a process for preparing such phenylpyrimidine derivatives, liquid crystal compositions containing said derivatives as active ingredient, and liquid crystal elements using such compositions.
2. Description of the Prior Art
Twisted nematic (TN) type display systems are most popularly used for the liquid crystal display elements at present. This TN liquid crystal display system has many advantages such as low driving voltage and small power consumption, but this type of display is inferior to the luminous type display devices such as cathode-ray tube display, electroluminescent display and plasma display in respect of response speed. A new TN type display device having the angle of twist regulated to the region of 180.degree. to 270.degree. has been developed, but this device is still unsatisfactory in response speed. Many efforts have been and are being made for the improvement of TN type displays, but there has yet been realized no TN type display element with satisfactorily high response speed. A possibility of a remarkable improvement of response time is noticed in the new display system using ferroelectric liquid crystals which are studied in earnest recently (Clark et al: Applid. Phys. Lett., 36, 899, 1980). This system makes use of a chiral smectic phase such as chiral smectic C phase (hereinafter referred to as Sc* phase) which exhibits ferroelectric characteristics. Sc* phase is not the only phase which shows ferroelectric characteristics; it is known that chiral smectic F, G, H and I phases also exhibit ferroelectric characteristics.
The ferroelectric liquid crystal material used for the practically applied ferroelectric liquid crystal elements is demanded to meet many property requirements. With the present state of the art, it is impossible to satisfy all of these requirements by use of a single compound; it is necessary to use a ferroelectric liquid crystal composition obtained by mixing several liquid crystal compounds or non-liquid-crystal compounds.
Beside the ferroelectric liquid crystal compositions composed of ferroelectric liquid crystal compounds alone, it is also reported that a ferroelectric liquid crystal composition can be obtained by using as base material a compound or composition presenting a non-chiral smectic C, F, G, H or I phase (hereinafter referred to as Sc phase, etc.) and mixing therewith one or more compounds assuming a ferroelectric liquid crystal phase (Japanese Patent Application Kokai (Laid-Open) No. 195187/86). There is also a report on the preparation of a ferroelectric liquid crystal composition by using as base material a compound or composition presenting a Sc phase, etc., and mixing therewith one or more compounds which are optically active but exhibit no ferroelectric liquid crystal phase (Mol. Cryst. Liq. Cryst., 89, 327, 1982).
Reviewing these teachings synthetically, it is noted that a ferroelectric liquid crystal composition can be formed by using as base material one or more optically active compound no matter whether they assume a ferroelectric liquid crystal phase or not. However it is desirable that the optically active substance used presents a liquid crystal phase, and even when it doesn't present a liquid crystal phase, it has structural analogy to a liquid crystal compound so that it may be called a quasi-liquid crystal material. There is yet found however no liquid crystal material which exhibits enough spontaneous polarization for enabling high-speed response, is low in viscosity and presents a ferroelectric liquid crystal phase in a wide range of temperature including room temperature region.
Some of the compounds according to the present invention are included in the concepts of Japanese Patent Application Kokai Nos. 49/89 and 301667/89 and EP 0255219, but these prior applications merely give a notional description of the preparation processes of said compounds and make no particular reference to said compounds.
Also, part of the compounds of this invention are included in the concept of Japanese Patent Application Kokai No. 131444/90, but this application gives no concrete description about the properties and other features of said compounds. Further, the conceptional preparation process of this patent lacks practical utility since it necessitates the troublesome reaction and steps and also uses as starting material a compound having asymmetric carbon atoms as starting material a compound having asymmetric carbon atoms for the introduction of asymmetric carbon atoms, so that this process can not be an industrially advantageous technique.